1. Field of the Invention
The present invention relates to a catalytic heat exchanger and to a method of carrying out a catalytic reaction wherein gaseous or vaporized reactants are flowed into contact with a catalytic material.
2. Description Relative to the Prior Art
The catalytic heat exchangers disclosed in U.S. Pat. Nos. 4,162,290, and 4,256,783 comprise a reaction chamber having input and output ports through which a heat exchange fluid is introduced and withdrawn. A plurality of tubes disposed within the reaction chamber and adapted to circulate gaseous or vaporized reactants therethrough contain a catalytic material inside of the tube walls. As the heat exchange liquid is pumped through the reaction chamber and contacts the outside of the tubes, the desired catalytic reaction takes place within the tubes.
There are a number of disadvantages to the aforementioned prior art catalytic heat exchangers. First, in many cases when gaseous or vaporized reactants are put through a catalytic reaction, there is an increase or decrease in gas or vapor volume. For example, when methanol is decomposed to hydrogen and carbon monoxide (CH.sub.3 OH+heat.fwdarw.2H.sub.2 +CO) 2 mols of hydrogen and 1 mol of carbon monoxide are produced from one mol of methanol. However, no provision is made in these prior art exchangers for expansion or contraction of the gases. Second, in the prior art exchangers, the tubes are made of stainless steel and the catalyst is coated on ceramic pellets located inside the tubes. When heated, the stainless steel tubes expand more rapidly than the ceramic pellets, causing the pellets to become loose and abrade to dust, especially when subject to vibration as, for example, in an automobile catalytic converter system. Third, it is difficult to maintain a uniform temperature which promotes reaction specificity throughout the reaction chamber of these prior art exchangers. Fourth, replacement of the catalyst material in the prior art exchangers requires an expensive tube cleaning procedure. In some instances, where the tubes cannot be effectively cleaned, the tubes and tube support structure must be replaced.
U.S Pat. No. 4,246,235 discloses a horizontal flow catalytic reactor particularly useful as a catalytic recombiner for boiling water nuclear reactors. In this catalytic reactor, a foraminous retaining means adapted to be easily filled and emptied with particle-form catalytic material occupies the complete cross-section of the reaction zone available for the flow of the reactant gases. The principal disadvantage of this apparatus is that the reacting gases pass through the catalytic material only once. This requires a very high pressure for any useful volume of catalyst and temperature uniformity across the volume of catalyst is difficult to maintain.